PROCESS TO PRODUCE LIGHTWEIGHT OLEFINS
Description The present invention relates to a process for producing light olefins rich in ethylene from methanol and dimethyl ether. A remarkable growth in the production of synthetic fibers, plastics and rubber has taken place in recent decades. This growth, to an extremely large extent, has been supported and stimulated by an expanding supply of cheap petrochemical raw materials, such as ethylene, propylene and other olefins of four and five carbon atoms. Along with this growth there has been an increasing demand for alkylation, made by reacting olefins with isobutane, for use as a component of high octane gasoline. The growing demand for olefins, particularly ethylene, propylene and butenes, has of course leading to periods of shortage that have in turn led to substantial increases in the price of the materials used to feed the commercialized technologies. These feed materials are largely C2-C4 paraffins co-produced with natural gas and / or straight run paraffinic naphtha. These feedstocks can be substantially more expensive than methane, making it desirable to provide efficient means for converting methane to olefins. The conversion of methane to methanol, followed by the conversion of methanol to light olefins, is among the most economical routes to make light olefins from methane. In this regard, it is known that methanol or methyl ether can be catalytically converted into mixtures of olefin-containing hydrocarbons by contact under certain conditions with particular types of crystalline zeolite materials. U.S. Patent Nos. 4,025,575 and 4,038,889, for example, disclose both processes by which methanol and / or methyl ether can be converted to an olefin-containing product on a zeolite catalyst with a constriction index of 1-12, particularly ZSM-5. In fact, ZSM-5 converts methanol and / or methyl ether into hydrocarbons containing a relatively high concentration of light olefins, with a long life of the catalyst before the regeneration of the catalyst becomes necessary. It has also been reported that other types of zeolite catalysts can be used to convert methanol and / or methyl ether into hydrocarbon products containing olefins, containing even higher proportions of light olefins than those previously obtained with ZSM-5. For example, U.S. Patent No. 4,079,095 discloses that zeolites of the erionite-ofretite-chabazite type, and especially ZSM-34, can be usefully employed to promote the conversion of methanol and / or methyl ether into products comprising a greater amount of ethylene and propylene. However, although the erionite-ofretite-chabazite type catalysts are highly selective for the production of light olefins, such smaller pore zeolites tend to age rapidly compared to ZSM-5 when used for conversion of methanol / methyl ether. U.S. Patent Nos. 4,677,242 and 4,752,651 disclose the conversion of methanol to C2-C4 olefins on various silicoaluminophosphates and "non-zeolitic molecular sieves" (such as metal aluminophosphates) and teach that the addition of diluents, such as aromatic materials , having a kinetic diameter greater than the pore size of the molecular sieve, increases the ratio of ethylene to propylene in the product. T. Mole, G. Bett and D.J. Seddon, Journal of Catalysis 84, 435 (1983) disclose that the presence of aromatic compounds can accelerate the conversion catalyzed by zeolite of methanol into hydrocarbons. The article reports ethylene yields of 5 to 22% when catalytically converting methanol in the presence of benzene or toluene to ZSM-5 at sub-atmospheric pressure, 279 to 350 * C, and 100% methanol conversion. United States Patent No. 4, 499,314 discloses that the addition of various promoters, including aromatic compounds, such as toluene, accelerates the conversion of methanol to hydrocarbons on zeolites, such as ZSM-5, which have a sufficient pore size to allow sorption and diffusion of the promoter. In particular, the aforementioned patent 4,449,314 teaches that the increased conversion resulting from the addition of the promoter allows the use of conditions of lower severity, particularly lower temperatures, which increases the yield of lower olefins (column 4, lines 17-22) . Thus, in Example 1 of the patent, the addition of toluene as a promoter reduces the temperature required to achieve full methanol conversion of 295 to 288 * C while increasing the ethylene yield from 11 to 18% by weight. In the examples of said patent 4,499,314, the methanol feed material is diluted with water and nitrogen such that the partial pressure of methanol is less than 2 psia. Despite the existence of methanol conversion processes using a variety of zeolite catalysts and process conditions, there is a continuing need to develop new suitable methods for converting an organic charge comprising methanol and / or dimethyl ether selectively into products of light olefins, and in particular ethylene. An objective of the present invention, therefore, is to meet this need. The present invention resides in a process for converting methanol and / or dimethyl ether into a product containing C2-C4 olefins, comprising the step of contacting a feed containing methanol and / or dimethyl ether with a catalyst comprising a material crystalline porous, the contact passage being conducted in the presence of a co-fed aromatic compound under conversion conditions that include a temperature of 350 to 480 ° C and a partial pressure of methanol in excess of 10 psia (70 kPa), the material crystalline porous having a pore size greater than the critical diameter of the aromatic compound and the aromatic compound being capable of alkylation by the methanol and / or the dimethyl ether under the conversion conditions. Preferably, the molar ratio of methanol and / or dimethyl ether to aromatic compound is greater than 5: 1 and preferably is less than 300: 1. More preferably, the molar ratio of methanol and / or dimethyl ether to aromatic compound is from 10: 1 to 150: 1. Preferably, the conversion conditions include a temperature of 400 to 460 * C. Preferably, the conversion conditions are such that the conversion rate of methanol is less than 90%, and more preferably less than 80%. Preferably, the porous crystalline material has a pore size between 5 and 7 Angstroms. Preferably, the porous crystalline material is an aluminosilicate zeolite and most preferably ZSM-5. Preferably, the catalyst has an alpha value of less than 10 and more preferably less than 2.
Preferably, the porous crystalline material has a diffusion parameter for 2,2-dimethylbutane of 0.1-20 sec "1, when measured at a temperature of 120 * C and a pressure of 2,2-dimethylbutane of 60 torr (8 kPa) Preferably, the porous crystalline material has a diffusion parameter of 0.2-5 sec "1. Preferably, the catalyst contains coke or an oxide modifier selected from oxides of boron, magnesium, silicon and, most preferably, phosphorus. Preferably, the catalyst contains 0.05 to 20% by weight, and more preferably 1 to 10% by weight of the coke or the oxide modifier in an elemental base. The present invention provides a process for selectively converting methanol and / or dimethyl ether to C2-C4 olefins, particularly ethylene, on a porous crystalline catalyst and in the presence of a co-fed co-feed having a critical diameter smaller than the size of pore of the catalyst and that is capable of undergoing alkylation by methanol and / or dimethyl ether under the conversion conditions. The process of the present invention is distinguished from that of U.S. Patent No. 4,499,314 discussed above in which substantially water-free methanol feed is contacted with a zeolite catalyst, such as ZSM-5, in the presence of a aromatic reactant at a relatively high temperature of 350 to 480 ° C and a relatively high partial pressure of methanol in excess of 10 psia (70 kPa) Methanol may contain various amounts of water but, unlike other processes, it is not necessary co-feeding of water vapor and does not have a harmful effect.In addition, the process conditions are preferably controlled so that the conversion of methanol is less than 90% and more preferably less than 80%. it is found that ethylene selectivities in excess of 30% by weight can be achieved in comparison with the ethylene selectivities of 18-25% by weight reported in the aforementioned 4,499,314 patent. Although it is not desired to be limited by any theory of operation, it is believed that the ethylene selectivity of the process of the invention derives from the observation that virtually all of the ethylene produced via the partial catalytic conversion of methanol to light olefins using zeolite catalysts is derived from the retro-disintegration (retro-cracking) of ethyl-aromatic intermediates. The formation of such ethyl aromatic intermediates is believed to be facilitated in the present process by a mechanism in which the aromatic compound effectively acts as a catalyst in the conversion of two molecules of methanol into one molecule of ethylene. In this way, the methylation of aromatics with methanol in zeolites, such as ZSM-5, is a rapid, well-known reaction. The polymethylbenzenes produced are stable but are too large to easily exit the pores of the catalyst. Although relatively slow, the next expected reaction of an aromatic polymethyl is skeletal isomerization to a mixed aromatic methyl ethyl. Once formed, the aromatic ethyl tends to a rapid disintegration reaction to form ethylene and the co-catalytic aromatic ring. In the process described in U.S. Patent No. 4,499,314, the toluene co-feed is merely a promoter for initiating the reaction. When methanol is converted to the same catalyst at 288 ° C in the absence or in the presence of toluene, there is little difference in the ethylene selectivity obtained In addition, a process using the same catalyst as that used in the United States patent No 4,499,314, operating at the same temperature (288-295 * C), at high pressure (90 psia) and more than 50% conversion of methanol produces little or no olefins In contrast, the process of the invention unexpectedly retains the selectivity Almost constant ethylene at 80% methanol conversion at reactor pressures approaching 100 psia., the invention described in the present sample unexpectedly that co-feeding aromatics can be used as a novel control handle for the ethylene yield. Increasing the amount of co-feed aromatics from 0 to 5% by weight increases the selectivity to ethylene at constant conditions and conversion. Because only a small amount is required, using an aromatic co-feed as a control handle is easily achieved at low cost to the operator. Any methanol feed comprising at least 60% by weight of methanol can be used to provide methanol for use in this invention. Substantially pure methanol, such as industrial grade anhydrous methanol, is eminently suitable. Crude methanol, which usually contains 12 to 20% by weight of water, or even a more dilute solution, can also be used. However, the presence of water as a diluent to reduce the partial pressure of methanol is not required. Trace amounts (less than 1% by weight) of non-aromatic organic impurities, such as higher alcohols, aldehydes, or other oxygenates, have little effect on the conversion reaction of this invention and may be present in the methanol feed. Instead of, or in addition to, methanol, the feed of non-aromatic reagents may comprise dimethyl ether. When this component is present, it can comprise up to 100% of the feed of non-aromatic organic reagents, or the dimethyl ether can be mixed with methanol to form the non-aromatic reactive feed. For purposes of the present invention, it is contemplated to directly convert methanol and / or dimethyl ether into the feed in a hydrocarbon mixture characterized by a high content of light olefins, especially ethylene. Such amounts of dimethyl ether can be formed concomitantly in the conversion reaction; however, they can be recovered and recycled by feeding fresh organic reagents. • Aromatic co-feeding can come from a wide variety of sources, and even substantial amounts of non-aromatic organic components have little impact on the catalytic role of aromatic co-feed. For this reason, any organic feed stream containing more than 10% by weight aromatics, which have a critical diameter smaller than the pore size of the catalyst so that it can easily diffuse into the pores of the catalyst, is suitable for use as a catalyst. -feeding aromatics in the process of the invention. These include, but are not limited to, benzene, toluene, xylenes, C9 + reforming streams, light reformers, full-range reformers or any distilled fraction thereof, coker naphtha or any fraction thereof, FCC naphtha or any fraction distilled from it, and aromatics ded from mineral coal. Part of the aromatic compounds required can also be produced in-house by aromatization of the methanol feed. The presence of impurities, such as nitrogen and sulfur compounds, dienes and styrenes, in the aromatic component can be tolerated with little impact when using the embodiments of the invention in fluid or moving bed.
In a preferred embodiment, toluene constitutes part or all of the aromatic portion of the feedstock. The molar ratio of methanol and / or dimethyl ether to aromatic compound will normally be greater than 5: 1, since higher concentrations of aromatic compound lead to excessive coke formation, increased separation volumes and recycle traffic, and minimal gains in total chemical selectivities. Moreover, the molar ratio of methanol and / or dimethyl ether to aromatic compound is usually maintained below 300: 1, since lower concentrations of aromatic compound lead to little or no noticeable improvement in the ethylene selectivity of the process. However, the required amount of aromatic compound is reduced as the pressure increases, so that at a high pressure it may be possible to achieve a significant improvement in ethylene selectivity with molar ratios of methanol and / or dimethyl ether to aromatic compound above of 300: 1. Preferably, the molar ratio of methanol and / or dimethyl ether to aromatic compound is from 5: 1 to 250: 1. The catalyst used in the process of the invention is a porous crystalline material having a pore size greater than the critical diameter of the aromatic compound co-feed. Preferred catalysts are porous crystalline materials having a pore size between 5 and 7 Angstroms and in particular intermediate pore size aluminosilicate zeolites. A common definition for intermediate pore zeolites involves the constriction index test, which is described in U.S. Patent No. 4,016,218. In this case, the intermediate pore size zeolites have a constriction index of 1-12, as measured in the zeolite alone without the introduction of modifiers and before any treatment to adjust the diffusivity of the catalyst. In addition to medium pore size aluminosilicates, other acidic pore metalosilicates, such as silicoaluminophosphates (SAPOs), can be used in the process of the invention. Particular examples of suitable medium pore zeolites include ZSM-5, ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-35, ZSM-48, and MCM-22, with ZSM-5 and ZSM being particularly preferred. -eleven. ZSM-5 zeolite and its conventional preparation are described in U.S. Patent No. 3,702,886. ZSM-11 zeolite and its conventional preparation are described in U.S. Patent No. 3,709,979. ZSM-12 zeolite and its conventional preparation are written in U.S. Patent No. 3,832,449. ZSM-23 zeolite and its conventional preparation are described in U.S. Patent No. 4,076,842. Zeolite ZSM-35 and its conventional preparation are described in U.S. Patent No. 4,016,245. ZSM-48 zeolite and its conventional preparation are taught by U.S. Patent No. 4,375,573. The MCM-22 zeolite is disclosed in U.S. Patent Nos. 5,304,698; 5,250,277; 5,095,167; and 5,043,503. In order to increase the concentration of aromatics in the pores of the catalyst without increasing the molar ratio of aromatic to methanol, it may be desirable to use a catalyst having increased diffusional barriers. In particular, it may be desirable to employ a catalyst comprising a porous crystalline material having a diffusion parameter for 2,2-dimethylbutane of 0.1-20 sec "1, preferably 0.1-15 sec" 1, and most preferably 0.2- 5 sec "1 when measured at a temperature of 120 * C and a pressure of 2, 2-dimethylbutane of 60 torr (8 kPa) As used herein, the diffusion parameter of a particular porous crystalline material is defined as D / r2xl06, where D is the diffusion coefficient (cm2 / sec) and r is the radius of the crystal (cm) The required diffusion parameters can be derived from the sorption measurements, provided that the assumption is made that the flat sheet model describes the diffusion process., for a given sorbate charge Q, the value Q /, where Q8 is the equilibrium sorbate charge and is mathematically related to (Dt / r2), where t is the time (sec) required to reach the sorbate charge Q Graphical solutions to the flat sheet model are given by J. Crank in "Mathematics of Diffusion", Oxford University Press, Ely House, London, 1967. The intermediate pore zeolites described above as preferred for the process of the invention may have values of the diffusion parameter in excess of the required range of 0.1-20 sec. "1 However, the diffusion parameter can be controlled or modified to the value required by a variety of methods, for example, the required diffusivity can be achieved by using forms of large crystal (greater than 1 miera) of the porous crystalline material, depositing coke on the material before using it in the process (as described in U.S. Patent No. 5,097,543) and / or combining the material with the An oxide modifier, preferably selected from the group consisting of oxides of boron, magnesium, calcium, silicon, lanthanum and, most preferably, phosphorus. The total amount of coke or oxide modifier, as measured in an elemental base, may be between 0.05 and 20% by weight, and preferably between 1 and 10% by weight, based on the weight of the final catalyst. Alternatively, the required diffusional constriction can be achieved by severely treating the catalyst with steam to effect a controlled reduction in the micropore volume of the catalyst to not less than 50%, and preferably to 50-90%, based on of the catalyst without steam treatment. The reduction in the volume of micropores is derived by measuring the n-hexane adsorption capacity of the catalyst, before and after the steam treatment, at 90 ° C and a n-hexane pressure of 75 torr. The application of water vapor to the porous crystalline material is carried out at a temperature of at least 850 ° C, preferably 950 to 1.075 ° C, and most preferably 1,000 to 1,050 ° C for 10 minutes to 10 hours, preferably 30 minutes to 5 hours To effect the desired controlled reduction in diffusivity and micropore volume, it may be desirable to combine the porous crystalline material, before steam treatment, with a phosphorus modifier.The total amount of the phosphor modifier , which will normally be present in the catalyst in oxide form, as measured in an elemental base, may be between 0.05 and 20% by weight, and preferably is between 1 and 10% by weight, based on the weight of the final catalyst Where the modifier is phosphorus, the incorporation of the modifier into the catalyst of the invention is conveniently achieved by the methods described in U.S. Patent Nos. 4,356,338; 5,110,776; and 5,231,064. Similar techniques known in the art can be used to incorporate other modifying oxides in the catalyst of the invention. The porous crystalline material used in the process of the invention can be combined with a variety of binder or matrix materials resistant to the temperatures and other conditions employed in the process. Such materials include active and inactive materials such as clays, silica and / or metal oxides such as alumina. The latter may be as occurs naturally or be in the form of gelatinous precipitates or gels, including mixtures of silica and metal oxides. The use of a material that is active tends to change the conversion and / or selectivity of the catalyst and therefore is generally not preferred. Inactive materials suitably serve as diluents to control the amount of conversion in a given process so that products can be obtained economically and orderly without employing other means to control the rate or rate of the reaction. These materials can be incorporated into natural occurring clays, for example bentonite and kaolin, to improve the crushing resistance of the catalyst under commercial operating conditions. Said materials, ie clays, oxides, etc., function as binders for the catalyst. It is desirable to provide a catalyst that has good crush resistance because in commercial use it is desirable to prevent the catalyst from breaking in powder-like materials. These clay and / or oxide binders have been used normally only for the purpose of improving the crushing strength of the catalyst. Naturally occurring clays that can be formed into composite materials with porous crystalline material include the family of montmorillonite and kaolin, which families include the sub-bentonites and kaolins commonly known as Dixie, McNamee, Georgia and Florida, or others materials in which the main mineral constituent is haloisite, kaolinite, dickite, nacrite or anauxite. Such clays can be used in the raw state, as originally obtained in the mine or initially subjected to calcination, acid treatment or chemical modification. In addition to the above materials, the porous crystalline material can be formed into composite material with a porous matrix material such as silica-alumina, silica-magnesia, silica-zirconia, silica-toria, silica-berilia, silica-titania, as well as ternary compositions such as silica-alumina-toria, silica-alumina-zirconia, silica-alumina-magnesia and silica-magnesia-zirconia. The relative proportions of the porous crystalline material and the inorganic oxide matrix vary widely, with the content of the former varying from 1 to 90% by weight and, more usually, particularly when the composite material is prepared in the form of beads, in the range from 2 to 80% by weight of the composite material. Preferably, the binder material comprises silica or a kaolin clay. Methods for preparing silica-bound zeolites, such as ZSM-5, are described in U.S. Patent Nos. 4,582,815; 5,053,374; and 5,182,242. A particular process for agglutinating ZSM-5 with a silica binder involves an extrusion process. The porous crystalline material can be combined with a binder in the form of a fluidized bed catalyst.
This fluidized bed catalyst may comprise clay in its binder, and may be formed by a spray drying process to form catalyst particles having a particle size of 20 to 200 microns. The catalyst employed of the invention preferably has an extremely low acid activity. Using the acid activity alpha test disclosed in the Journal of Catalysis, vol. 61, p. 395 (1980), the catalyst of the invention preferably has an alpha value of less than 10, more preferably less than 2. The process of the invention is preferably carried out in a catalyst bed in motion or fluid, with oxidative regeneration keep going. The extension of the load with coke can then be controlled continuously varying the severity and / or the frequency of the regeneration. The process of the present invention is conducted at a relatively high temperature between 350 and 500 ° C, preferably between 400 and 480 ° C, then, as will be illustrated by the following examples and in a manner contrary to the teachings of the US patent. United States No. 4,499,314, it has been found that such a temperature range is critical for the selective production of lower olefins. Although it is not desired to be limited by any theory of operation, it is believed that such a relatively high temperature is essential for the isomerization of the skeleton and the disintegration of the polymethylbenzene intermediates produced, while higher temperatures lead to excessive coke formation. . The process of the invention is advantageous in that it is found that the selectivity to lower olefins of the product is generally independent of the partial pressure of methanol, so that the need in the processes of the prior art to reduce the methanol pressure by the addition of diluents or by operation at reduced pressure can be avoided. The ability to operate at higher methanol partial pressures also allows to increase the absolute yield per pass of the olefin product. A partial pressure of methanol suitable for use in the process of the invention is in excess of 10 psia (70 kPa), preferably 15 to 150 psia. In addition, it is desirable that the conversion conditions be controlled so that the level of methanol conversion is less than 90%, and preferably less than 80%, then, at higher conversion levels, reactions that compete with the methylation of aromatics, such as alkylation of olefins and / or oligomerization to produce C5 + isoolefins and / or conversion of olefins to aromatics and paraffins, reduce the selectivity to ethylene and propylene. Of course, adequate control of the methanol conversion can be achieved by varying the hourly speed space by weight, which typically can vary between 0.1 and 100, preferably between 0.1 and 10. The process of the invention converts methanol and / or dimethyl ether in a stream of light olefins in which the ethylene comprises more than 40% by weight, and typically more than 50% by weight of the C2-C4 olefins, and in which the ethylene comprises more than 90% by weight, preferably more than 95% by weight of component C2. In addition to the light olefins, a product of the process are xylenes, which comprise a high proportion of the para isomer, particularly where a diffusionally constricted catalyst is employed as described above. The invention will now be described more particularly in the following examples and the accompanying drawings, in which: Figure 1 is a graph depicting the selectivity to ethylene against the conversion of methanol to the catalyst of Example 1, when used to convert methanol in the presence of varying amounts of water and toluene; Figure 2 is a graph comparing the selectivity to ethylene with the temperature for the catalyst of Example 1, when used to convert methanol in the presence of toluene to molar ratios of methanol to toluene of 10: 1 and 155: 1. Figures 3 and 4 are graphs similar to Figure 3, but comparing the conversion of toluene and the percentage by weight of ethylene / p-xylene, respectively, with temperature, using the same catalyst and the same molar ratios of methanol to toluene. Figure 5 is a graph comparing the selectivity to ethylene with the conversion of methanol for the catalyst of Example 1 to a molar ratio of methanol to toluene of 55: 1, with that of the catalyst of Example 4 at a molar ratio of methanol to toluene of 26: 1. Figure 6 is a graph comparing the selectivity to olefins with the temperature at partial methanol pressures of 15 and 90 psia for the catalyst of Example 5. Figure 7 is a graph comparing the effects of methanol partial pressure on the selectivity to olefins at different temperatures using the catalyst of Example 5. In the examples, volume measurements of micropores (n-hexane) were performed on a computer-controlled thermo-gravimetric analyzer (Vista / Fortran) duPont 951. The isotherms were measured at 90 ° C and the adsorption values were taken at 75 torr of n-hexane. The diffusion measurements were made on a TA Instruments 2950 thermo-gravimetric analyzer, with a 2000 thermal analysis controller, a gas switching accessory and an automatic sample changer. Diffusion measurements were made at 120 ° C and 60 torr of 2,2-dimethylbutane The data was plotted as intake versus square root of time Fixed bed catalytic tests were conducted using a downflow reactor of 3/8"(1 cm) in external diameter, equipped with a thermocouple. Methanol, water and aromatics were pumped into the reactor by a vaporizer equipped with a static mixer to gasify and intimately mix the feed materials upstream of the reactor. The reactor was equipped with a back-pressure regulator to allow the examination of products at a wide variety of temperatures, pressures and WHSVs. The total effluent from the reactor was analyzed, online, by means of gas chromatography. The conversion of methanol was calculated based on the formation of hydrocarbons only. The selectivities to the hydrocarbon product were calculated on a "water-free" basis. Example 1 Phosphoric acid, kaolin clay, and 450: 1 Si02 / Al203 ZSM-5 were formed in a slurry in water and spray dried to make a typical fluid bed catalyst. The catalyst was calcined in air at 510 'C. The finished catalyst contained 40% by weight of ZSM-5 and 4.5% by weight of phosphorus. This material has an n-hexane sorption of 33.5, a diffusion parameter of 27 sec "1, and an alpha value of 7. The catalyst was then treated with steam at 1,050'C for 0.75 hours in 1 steam atmosphere of water to produce a final catalyst having a diffusion parameter of 0.46 sec "1 and a n-hexane sorption of 30.6 mg / g. EXAMPLE 2 A first sample of 0.5 g of the steam-treated catalyst of Example 1 was used to convert a feed material of pure methanol to 0.5-10 WHSV, 430"C and 1 atmosphere of pressure. methanol conversions The ethylene selectivity of the hydrocarbon product is plotted versus the conversion of methanol in Figure 1. A second sample of 0.5 g of the steam-treated catalyst of Example 1 was used to convert a feed material at a 3: 1 molar ratio of methanol: water at 0.5-10 WHSV, 430'C and 1 atmosphere of pressure.A wide range of methanol conversions was obtained.The ethylene selectivity of the hydrocarbon product is plotted against the conversion of methanol in Figure 1. A third sample of 0.5 g of the steam-treated catalyst of Example 1 was used to convert a feed material to a 26: 1 molar ratio of methanol: toluene at 0.5-5 WHSV, 430 'C Y 1 atmosphere of pressure. A wide range of methanol conversions was obtained. The ethylene selectivity of the hydrocarbon product is plotted against the conversion of methanol in Figure 1. A fourth sample of 0.5 g of the steam-treated catalyst of Example 1 was used to convert a feed material to a molar ratio 3: 1 of methanol: toluene at 0.5-5 WHSV, 430 * C, and 1 atmosphere of pressure. A wide range of methanol conversions was obtained. The ethylene selectivity of the hydrocarbon product is plotted against the conversion of methanol in Figure 1. Figure 1 clearly shows that the addition of one mole of water vapor per 3 moles of methanol to the feed material leads to a negligible change in ethylene selectivity. In contrast, the addition of toluene in an amount as small as 1 mole of toluene per 26 mole of methanol leads to a great improvement in ethylene selectivity, particularly if the conversion of methanol is maintained below 90%. Example 3 An additional sample of 0.5 g of the steam-treated catalyst of Example 1 was used to convert a feed material to a 12: 1 molar ratio of methanol: toluene at 1 atmosphere of pressure, 0.5-5 WHSV, and various temperatures between 380 and 480 * C. A wide range of methanol conversions was obtained. From these data, the selectivity to ethylene, the conversion of toluene, and the weight percentage of ethylene / p-xylene to a methanol conversion of 70% were extracted at each temperature, and the results are plotted in figures 2 to 4. The test was then repeated with a feed material having a 155: 1 molar ratio of methanol: toluene and again the data are plotted in figures 2 to 4. Figures 2 to 4 show that the feed material to a 155: 1 molar ratio of methanol: toluene does not have sufficient co-feed of aromatics at any temperature to produce both ethylene and the feedstock at a 12: 1 molar ratio of methanol: toluene. Moreover, as the temperature rises, the selectivity to ethylene is rapidly reduced by feeding at a 155: 1 molar ratio of methanol: toluene. Figures 2 to 4 also show that for the feed material at a 12: 1 molar ratio of methanol: toluene, the selectivity to ethylene is constant with temperature, but the ethylene / p-xylene ratio in the product is rapidly reduced with the increase in temperature. In this way, catalyst control, feeding and temperatures allow a product to choose from a wide range of ethylene: p-xylene ratios in the product. Example 4 A sample of the untreated phosphorus-treated catalyst of Example 1 was steam-treated at 870 ° C for 6 hours in 1 atmosphere of steam to produce a catalyst having a diffusion parameter of 31. sec "1 and a n-hexane sorption of 34.9 mg / g 0.5 g of this catalyst were used to convert a feed material to a 26: 1 molar ratio of methanol: toluene at 0.5-10 WHSV, 430 * C , and 1 atmosphere of pressure A large range of methanol conversions was obtained and the ethylene selectivity of the hydrocarbon product is plotted versus the conversion of methanol in Figure 5. As a comparison, an additional sample of the steam treated catalyst of water of Example 1 was used to convert a feed material to a 55: 1 molar ratio of methanol: toluene under the same conditions and again the selectivity to ethylene versus the methanol conversion in Figure 5 is plotted. Figure 5 demonstrates the relationship between the amount of the aromatic co-feed and the diffusivity of the catalyst. The 55: 1 molar feed data with the diffusion restricted catalyst of Example 1 are essentially the same as the 26: 1 molar feed data with less diffusion restricted catalyst of Example 4. This shows that less co-feeding is required. aromatics to achieve a given distribution of the product with a more restricted catalyst in diffusion than that required with a less restricted catalyst in diffusion. Example 5 A commercially available FCC additive catalyst containing 25% by weight of ZSM-5 with a molar ratio of silica to alumina of 26: 1 and 3% by weight of phosphorus, was used in this example. The catalyst had been pre-treated with steam at 1,450'F (790 * C) for 4 hours and had an alpha value of 3, a diffusion parameter of 25 and an n-hexane sorption of 25 mg / g. The catalyst was used to convert a mixture of 90% by weight of methanol and 10% by weight of toluene (molar ratio methanol: toluene of 26: 1) at methanol partial pressures of 15 psia (103 kPa) and 90 psia (620 kPa) and at a methanol conversion level of 80%. Various temperatures between 210 and 490 ° C were used and the results are plotted in Figure 6. From Figure 6, it will be seen that the conversion of methanol in the presence of toluene is highly selective to olefins at temperatures between 350 and 480 ° C and that the selectivity to olefins is generally independent of the partial pressure of methanol, especially at temperatures of 400 and 450'C. Example 6 (Comparative) A catalyst of ZSM-5, bound with alumina, containing 65% by weight of ZSM-5 with a molar ratio of silica to alumina of 26: 1, which had been treated with steam at 515 ° C for 1 hour was used in this example. The catalyst had an alpha value of 100, a diffusion parameter of 1,000 and a n-hexane sorption of 77 mg / g. The catalyst was used to convert (a) a mixture of 90% by weight of methanol and 10% by weight of toluene (molar ratio methanol: toluene of 26: 1) and (b) pure methanol at a temperature of 270 ° C and a methanol conversion level of 50% and the results are listed in Table 1. From Table 1, it will be seen that at this low temperature the yield of light olefins is marginally lower with the toluene co-feed than with the feed of pure methanol.
Table 1
Example 7 The catalyst of Example 5 was used to convert a mixture of 90% by weight of methanol and 10% by weight of toluene (molar ratio methanol: toluene of 26: 1) at various temperatures and pressures. The total selectivity to olefins under each condition at a methanol conversion level of 80% is shown in Figure 7. The figure clearly shows that at lower temperatures, the effect of the pressure on the total selectivity to olefins becomes more and more pronounced Additionally, these results re-emphasize that the total selectivity to olefins is a strong function of temperature.